Liquid crystal display devices having a touch sensor in a picture unit or a pixel are known to public. As a sensing method for such liquid crystal display devices, three methods: a photo sensor method, a contact-point (touch) method, and a capacitance method have been put to practical use.
FIG. 10 shows a configuration example of a display region having a photo sensor type touch sensor.
The configuration of an “n”-th row in the display region of the liquid crystal display panel is extracted and shown in FIG. 10. Arranged in the “n”-th row are a plurality of picture units PIX . . . , which are partitioned by a gate wire Gn, a source wire S (Sm to Sm+3 are shown in the figure), and a storage capacitance wire Csn, and one or more sensor circuits 102 that are connected to a reset wire Vrstn and a read-out control wire Vrwn.
The picture unit PIX includes a TFT 101 as a switching element, a liquid crystal capacitance CL, and a storage capacitance CS. A gate of the TFT 101 is connected to the gate wire Gn, a source of the TFT 101 is connected to a source wire S, and a drain of the TFT 101 is connected to a picture unit electrode 103, respectively. The liquid crystal capacitance CL is a capacitance in which a liquid crystal layer is interposed between the picture unit electrode 103 and a common electrode “com.” The storage capacitance CS is a capacitance in which an insulating film is interposed between the picture unit electrode 103 or the drain electrode of the TFT 101 and the storage capacitance wire Csn. A fixed voltage is applied to the common electrode “com” and the storage capacitance wire Csn, respectively, for example.
An appropriate number of the sensor circuits 102 are provided such as one sensor circuit 102 per a picture unit PIX or a pixel (a set of RGB picture units PIX . . . , for example), and the sensor circuit 102 includes an output amp 102a, a photo diode 102b, and a capacitance 102c. The output amp 102a is formed of a TFT. A gate of the output amp 102a is connected to an electrode called a node netA here, a drain of the output amp 102a is connected to one source wire Sm+1, and a source of the output amp 102a is connected to another source wire Sm, respectively. An anode of the photo diode 102b is connected to the reset wire Vrstn, and a cathode of the photo diode 102b is connected to the node netA, respectively. One end of the capacitance 102c is connected to the node netA, and the other end is connected to the read-out control wire Vrwn, respectively.
The sensor circuit 102 performs touch sensing by using a period outside the period for writing data signals to the picture units PIX in order to detect the existence of a shadow created when a fingertip approaches or touches the panel. After resetting a voltage of the node netA by a voltage of the reset wire Vrstn through the photo diode 102b, a voltage that appeared in the node netA according to the intensity of light received at the photo diode 102b is output from the source of the output amp 102a as a sensor output voltage Vo by using a voltage increase of the node netA due to the voltage variation of the read-out control wire Vrwn. The sensor output voltage Vo is output to a sensor read-out circuit outside the display region through a sensor output wire Vom, which uses the source wire Sm+1. Here, the output amp 102a functions as a source follower. Further, here, the source wire Sm connected to the drain of the output amp 102a functions as a sensor power supply wire Vsm, which is applied with a fixed voltage when detecting light.
Next, FIG. 11 shows a configuration example of a display region having a contact-point type touch sensor.
This is a configuration in which the sensor circuit 102 of FIG. 10 is replaced with a sensor circuit 202.
The sensor circuit 202 includes a read-out TFT 202a and a vertical electrode switch 202b. A gate of the read-out TFT 202a is connected to a read-out signal wire Vrdm, a drain of the read-out TFT 202a is connected to one of the electrodes of the vertical electrode switch 202b, and a source of the read-out TFT 202a is connected to the sensor output wire Vom, respectively. The other electrode of the vertical electrode switch 202b is constituted of the common electrode “com,” and is applied with a voltage Vcom.
In the sensor circuit 202, when the panel is pressed by a fingertip, one electrode and the other electrode of the vertical electrode switch 202b come in contact with each other to form a contact point. Here, when the read-out TFT 202a is turned on by applying a voltage from the read-out signal wire Vrdm using a period outside the period for writing data signals to picture units PIX, the voltage Vcom is output to the sensor output wire Vom through the vertical electrode switch 202b and the read-out TFT 202a so that touch sensing can be performed.
Next, FIG. 12 shows a configuration example of a display region having a capacitance type touch sensor.
This is a configuration in which the sensor circuit 102 of FIG. 10 is replaced with a sensor circuit 302.
The sensor circuit 302 includes an output amp 302a, a photo diode 302b, and capacitances 302c and 302d. The output amp 302a is formed of a TFT. A gate of the output amp 302a is connected to an electrode called the node netA, a drain of the output amp 302a is connected to the source wire Sm, and a source of the output amp 302a is connected to the source wire Sm+1, respectively. An anode of the photo diode 302b is connected to the reset wire Vrstn, and a cathode of the photo diode 302b is connected to the node netA, respectively. One end of the capacitance 302c is connected to the node netA, and the other end is connected the read-out control wire Vrwn. One end of the capacitance 302d is connected to the node netA, and the other end is constituted of the common electrode “com.”
The sensor circuit 302 performs touch sensing by detecting a change in a capacitance value Ccvr of the capacitance 302d due to a pressing force applied on the panel by a fingertip by using a period outside the period for writing data signals to picture units PIX. The photo diode 302b is provided to drive the sensor circuit 302 as a photo sensor circuit in a manner similar to the sensor circuit 102, but its diode characteristic is used when driving the sensor circuit 302 as a touch sensor circuit. After a voltage of the node netA is reset through the photo diode 302b, a voltage of the read-out control wire Vrwn is changed, and as a result, the voltage of the node netA becomes a value in accordance with the capacitance 302c and the capacitance value Ccvr of the capacitance 302d determined by an applied pressing force, and therefore, a voltage appeared in the node netA is output from the source of the output amp 302a as a sensor output voltage Vo, and is output to a sensor read-out circuit outside the display region through the sensor output wire Vom, which uses the source wire Sm+1. Here, the output amp 302a functions as a source follower. Here, the source wire Sm functions as a sensor power supply wire Vsm, which is applied with a fixed voltage.
Next, among the touch sensors described above, a touch sensor with a contact-point method configuration disclosed in Patent Document 1 is shown in FIG. 13.
FIG. 13 is a cross-sectional view of a liquid crystal display device when a finger of a user or the like is in contact therewith. The liquid crystal display device is configured such that a liquid crystal layer 3 is interposed between a bottom display plate 100 and a top display plate 200. In the bottom display plate 100, a pixel layer 115 is formed on an insulating substrate 110. A pixel, a sensing part, and the like are formed in the pixel layer 115, and input terminal electrodes 196 of a sensing element of a contact sensing part are exposed over the pixel layer 115.
In the top display plate 200, light-shielding members 220 are formed on a substrate 210. The light-shielding members 220 prevent light leakage from an area between respective pixels. A plurality of color filters 230 are formed on the substrate 210 and the light-shielding members 220. A cover film 250 is formed on the color filters 230 and the light-shielding members 220 to cover the color filters 230 and to planarize the surface. On the cover film 250, a plurality of projections 240, which are made of an organic material or the like, are formed. The projections 240 are formed corresponding to the positions in which the input terminal electrodes 196 of a sensing element are formed. A common electrode 270 is formed on the cover film 250 and the projections 240. The two display plates 100 and 200 are supported by a plurality of bead spacers 320, and a certain distance of the range of 0.1 μm to 1.0 μm is maintained between the common electrode 270, which surrounds the projections 240, and the input terminal electrodes 196.
The common electrode 270, which surrounds the projections 240, and the input terminal electrodes 196 constitute a switch of the contact sensing part.
The top display plate 200 is pressed by a contacting pressure, and the common electrode 270 surrounding the projections 240 of the contacted position becomes electrically and physically connected to the input terminal electrodes 196 of the bottom display plate 100. As a result, a common voltage Vcom is transmitted to the input terminal electrodes 196, and the sensing element supplies a sensing current.